RE: Overloading an engine
Greg,
I guess most model engine manufacturers do not have a PhD in rocket science...
So, as engineers, they would usually just 'slap together' combos that work.
Occasionally; especially with an engine like no other, like this RCV; some variables do act together, through resonance, flow-speed, orifice sizes, Etc., to cause a nearly vertical, marked drop (or a peak) in torque, over a very narrow RPM span.
I would urge Juice to set that 18" prop to pitch numbers around 12", in 0.5" (or smaller) increments; and to take RPM measurements, to see where this drop actually happens. It is in the engine's internals, so we might not know exactly why it happens, however.
Ye hear, Juice???
As you can see from your graphs, since the left side and right side axes are now 'synchronized'; the torque (now in lbs.ft.) and the HP curves will intersect at 5,252.1 RPM, as I wrote in the previous posts.
"I love it when a plan comes together" (Now, who said that???)